The present invention relates generally to face seals for rotating machinery, and more particularly to a secondary seal for a face seal assembly.
Face seals are used to minimize leakage through a gap between two components, wherein such leakage is from a higher pressure area to a lower pressure area. Such seals have been used in rotating machinery, for example steam turbines and gas turbines. Face seals minimize the leakage of steam between a rotor and a stator in steam turbines and minimize the leakage of compressed air or combustion gases between a rotor and a stator in gas turbines.
Axial seals which have a moveable element, including face seals and aspirating seals, require a sliding secondary seal. This secondary seal must be capable of handling the same pressure ratio as the primary seal and must have minimal leakage. The secondary seal functions between two parts, one stationary and one which slides axially. The secondary seal is dry (non-lubricated) and must have low internal friction. In a gas turbine engine application, the secondary seal is also exposed to a severe operating environment, including a severe thermal environment and dust. The secondary seal must be capable of sealing between two parts while they deflect radially at different rates due to the surrounding hot gases with varying heat transfer coefficients. Prior art secondary seals typically use a plurality of arcuate segments or a piston ring as the secondary seal element, with multiple coil springs positioning the sealing element. This results in an unnecessarily high number of parts. Furthermore, at high gas velocities, dust can erode away the material of interrupted parts like coil springs which could result in seal failure.
Accordingly, there is a need for a face seal assembly having a secondary seal with a simple construction.
The above-mentioned need is met by the present invention, which provides a face seal assembly having an annular seal body mounted in an axially moveable relationship to a seal support structure. A piston ring is disposed between the annular seal body and the seal support structure forming a secondary seal. A first locator spring, which is an annular wave spring, is disposed between said seal support structure and the piston ring to urge the piston ring in an axial direction. Optionally, a second locator spring, also a wave spring, may be disposed between the piston ring and the seal support structure for urging the piston ring in a radial direction.